Cultured dairy foods

Soon after man began to use milk from animals he discovered that if it was not soon consumed it became sour and coagulated due to bacterial contamination of milk. People are believed to have started making fermented milks since early times, when they began to add small portions of common Streptococcus and Lactobacillus bacteria (often called "cultures") in warm milk from cows, sheep, goats, camels, or horses. These bacteria were found to be harmless lactic acid producers, thus especially effective in lowering the pH and in inhibiting growth of pathogenic organisms. So, it was possible to prevent milk from spoilage and to preserve it fresh for several days or weeks without refrigeration.

Having discovered that fermented milks were edible and delicious, tribes developed their own systems of handling the product. Thus, several varieties of fermented milk were developed and they are likely to have been introduced around the world as people migrated. Nowadays cultured buttermilk, acidophilus milk, sour cream and yogurt are sure to be among the most common fermented dairy products in the Western world. Less known products, such as kefir, koumiss, and new yogurts containing Bifidobacteria are likely to be more popular in Eastern Europe and Russia. Both kefir and koumiss contain from 1.0 to 2.5 percent alcohol, produced by yeasts that ferment lactose. Koumiss is typically made from mare's milk, while kefir from the milk of goats, sheep, or cows.

Nowadays the term "cultured milks" is used more widely throughout the world, because pure bacterial cultures are used in commercial

manufacture. Although, it is appropriate to use the words 'fermented' or 'sour' because lactic acid which causes sourness, is produced by fermentation of milk sugar — lactose.

Regardless of the type of cultured product, the same basic steps are necessary in processing through incubation. These steps are: (1) starter culture preparation, (2) treatment of milk, skim milk, cream, or other product (e.g., pasteurization and homogenization), (3) inoculation, and (4) incubation. If the product is to be fluid for drinking, the curd must be broken and agitated to produce a smooth homogeneous body. After incubation, and agitation if necessary, cooling is essential to stop the development of acidity. Liquid products are then ready for packaging, although some producers package yogurt and cultured cream before incubation.

Being excellent sources of calcium and protein, cultured dairy foods provide numerous potential health benefits to the human diet. In addition, they may help to establish and maintain beneficial intestinal bacterial flora and reduce lactose intolerance.

States as well as in Russia have increased in recent years more than those of any other item in the dairy produce. This is largely due to the introduction of fruit-flavoured yogurts and to an increased appreciation among consumers of the low-calorie, highly nutritional aspects of yogurt. Its most popular uses are as a between-meal snack, as a dessert, and as the noon meal.

Yogurt is made in a similar fashion to buttermilk and sour cream, but it requires different bacteria and temperature. Despite the different spellings used (yogurt, yoghurt, yahourt, yaourt, leben, mudzoon, luija, anddahi)l\\\e, product is fermented by Lactobacillus huigciricus and Streptococcus thermophilus in all countries except Turkey, where a yeast that ferments lactose is included. Being highly digestible, yogurt contains large quantities of protein, lactose, and B vitamins.

Traditionally, the product is said to have been made from milk concentrated by boiling. Today yogurt is made from homogenized whole, low-fat, or skim milk which are fortified with nonfat dry milk or fresh condensed skim milk in order to raise the total solids to 14-16 percent.

Skim milk without added solids has been found to contain only 8.5 to 9 percent total milk solids. However, by increasing the milk solids one can increase the body firmness of yogurt.

At the next step the mixture is heat-treated and then cooled to 45.6°-46.7°C. At this point a mixture of Lactobacillus bulgaricus and Streptococcus thermophilus cultures is added to the warm milk.

High incubation temperatures (41 to 45°C) are required by these bacteria, and their balance in the culture is determined by the temperature selected. Also, the ratio of one to the other in the inoculum must be controlled to produce favourable body and flavour characteristics. Usual ratios are 1:1 to 1:3, L. bulgaricus to S. thermophilus, though a harsh acid flavour may occur when L. bulgaricus predominates. Lactic acid, acetic acid, and acetaldehyde produced by these cultures were found to be important contributors to adequate yogurt flavour.

To obtain flavoured yogurt sugar and fruit are added to the obtained mixture, two different processing methods having been developed for the manufacturing of two popular types of fruit-flavoured yogurt known as Swiss and Sundae.

Fruit, flavouring, and colour are distributed throughout Swiss- or French-style yogurt. According to the technological process, the milk is allowed to incubate in large heated tanks. After coagulation occurs, the mixture is cooled, fruit or other flavours are added, and the product is placed in containers and immediately made ready for sale.

Fruit is placed at the bottom of the cup with yogurt on top to make Sundae-style yogurt. For its production the cultured mixture is poured1 into cups containing the fruit, held in a warm room until the milk coagulates (usually about 4 hours), and then moved to a refrigerated room.

Sundae-style yogurt causes fewer problems to the processor since fruit has a tendency to settle out in Swiss-style yogurt. Bacteria may attack portions of the fruit filling of Swiss-style yogurt, and dilution of fruit flavouring with yogurt reduces its preservative capacity.

Many yogurt manufacturers have added Lactocacillus acidophilus to their bacterial cultures, which is known to have possible health benefits in easing yeast infections and restoring normal bacterial balance to the intestinal tract of humans after antibiotic treatment.

Answer the questions:

1) Why did people begin to add some bacteria to milk?

2) What cultured dairy products are known in the world and where are they more popular?

3) What kind of milk is kefir and koumiss made from?

4) What fermentation process is the production of cultured milks based on?

5) What are the main steps of cultured milks production?

6) Why are cultured dairy foods important in human diet?

7) How did people identify buttermilk many years ago?

8) Is voeurt sold only in the USA now?

9) What substances is yogurt rich in?

10) How does Swiss-style yogurt differ from Sundae-style one?